Alnor HRU
Controls and monitors Alnor heat recovery ventilation units via Modbus RTU.
This template provides full Modbus RTU monitoring and control of Alnor HRU heat recovery ventilation units. It reads temperatures, airflow, humidity, CO2, fan speeds, and filter status. It also allows setting ventilation profiles, bypass mode, and fireplace demand.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 29, read and write
- Key readings
- Extract/Inlet/Exhaust/Supply temperatures · Supply and exhaust fan speed · Supply and exhaust air flow · CO2 indoor · Humidity indoor · Filter time remaining
- Available commands
- Ventilation speed setpoint · Fan speed profiles (Standby/1/2/3) · Bypass mode · Fireplace demand state
- Compatible models
- HRU-SlimAIR · HRU-PremAIR · HRU-MinistAIR · HRU-FlatAIR
- Last updated
Registers (29)
27 read, 12 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Actual Ventilation Speed | Read and write | ||||
| Error code | Read | ||||
| Exhaust fan speed | % | Read | |||
| Supply fan speed | % | Read | |||
| Extract Temperature | °C | Read | |||
| Inlet Temperature | °C | Read | |||
| Exhaust Temperature | °C | Read | |||
| Supply Temperature | °C | Read | |||
| Preheater status | Read | ||||
| Defrost | Read | ||||
| Bypass position | % | Read | |||
| Humidity indoor | % | Read | |||
| Filter status | Read | ||||
| Supply air flow | m³/h | Read | |||
| Exhaust air flow : | m³/h | Read | |||
| CO2 indoor | ppm | Read | |||
| Filter Time Remaining | days | Read | |||
| Bypass Mode | % | Read | |||
| Supply fan speed - Standby | % | Read and write | |||
| Exhaust fan speed - Standby | % | Read and write | |||
| Supply fan speed - Speed 1 | % | Read and write | |||
| Exhaust fan speed - Speed 1 | % | Read and write | |||
| Supply fan speed - Speed 2 | % | Read and write | |||
| Exhaust fan speed - Speed 2 | % | Read and write | |||
| Supply fan speed - Speed 3 | % | Read and write | |||
| Exhaust fan speed - Speed 3 | % | Read and write | |||
| Fireplace demand state | Read and write | ||||
| Reset Filter Time | Write | ||||
| Bypass mode | % | Write |
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Use cases
- Monitor supply and extract temperatures on a live dashboard to verify heat recovery efficiency.
- Create an alert when the remaining filter time drops below a threshold so maintenance can be scheduled proactively.
- Adjust ventilation speed profiles remotely when occupancy patterns change in a residential building.
- Track indoor CO2 and humidity levels over time to document compliance with indoor air quality standards.
- Activate fireplace demand mode remotely to ensure correct pressure balance when a fireplace is in use.
- Switch bypass mode during summer nights to enable free cooling without manual intervention on site.
Installation
Connect the Alnor HRQ-Modbus gateway to the HRU wireless control system following the Alnor installation manual.
Wire the RS-485 A and B terminals of the HRQ-Modbus gateway to the corresponding terminals on your ModbusCloud Gateway.
Set the Modbus RTU baud rate on the ModbusCloud gateway to 19200 with odd parity (8E1) to match the Alnor HRQ-Modbus defaults.
Configure the Modbus slave address on the HRQ-Modbus gateway and ensure it matches the address used in the ModbusCloud template.
Import the Alnor HRU template from the ModbusCloud template library and assign it to the correct gateway and slave address.
Verify communication by checking live temperature and fan speed readings on the ModbusCloud dashboard.
Things to watch for
Why do I get no response from the Alnor HRU on the Modbus bus?
The Alnor HRU requires the HRQ-Modbus gateway from Alnor to bridge its wireless control system to Modbus RTU. Without this gateway, the unit does not appear on the RS-485 bus. Also verify that the baud rate is set to 19200 and parity is set to odd (8E1).
Temperature readings show incorrect or very large values. What is wrong?
Temperature registers use float32 format spanning two consecutive Modbus registers. Ensure the word order (big endian or little endian) in your ModbusCloud gateway configuration matches the byte order expected by the Alnor HRQ-Modbus gateway.
Can I use this template with any Alnor HRU?
This template works only with Alnor HRU units equipped with the wireless control system. Older units without this system are not supported. Check your HRU model against the supported devices list in the template.
How do I reset the filter timer after replacing the filter?
The template includes a filter timer reset register. Write the reset command from the ModbusCloud dashboard or automation rule after physically replacing the filter in the unit.
More Alnor Systemy Wentylacji Sp. z o. o. templates
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